fix: fix error in sign_bytes

[arithmetic1728]

fix #851

If AuthorizedSession.post failed, we should throw an exception instead of calling the return base64.b64decode(response.json()["signedBlob"]) line.

[busunkim96]

self = <tests.test_impersonated_credentials.TestImpersonatedCredentials object at 0x7f3ac1d41710>

    def test_sign_bytes_failure(self):
        credentials = self.make_credentials(lifetime=None)

        with mock.patch(
            "google.auth.transport.requests.AuthorizedSession.request", autospec=True
        ) as auth_session:
            data = {"error": {"code": 403, "message": "unauthorized"}}
            auth_session.return_value = MockResponse(data, http_client.FORBIDDEN)

            with pytest.raises(exceptions.TransportError) as excinfo:
                credentials.sign_bytes(b"foo")
>           assert excinfo.match("{'error': {'code': 403, 'message': 'unauthorized'}")
E           AssertionError: Pattern "{'error': {'code': 403, 'message': 'unauthorized'}" not found in "Error calling sign_bytes: {'error': {'message': 'unauthorized', 'code': 403}}"

The order seems to change sometimes - I think loading the JSON into a dict would make the comparision stable.

[arithmetic1728]

self = <tests.test_impersonated_credentials.TestImpersonatedCredentials object at 0x7f3ac1d41710>

    def test_sign_bytes_failure(self):
        credentials = self.make_credentials(lifetime=None)

        with mock.patch(
            "google.auth.transport.requests.AuthorizedSession.request", autospec=True
        ) as auth_session:
            data = {"error": {"code": 403, "message": "unauthorized"}}
            auth_session.return_value = MockResponse(data, http_client.FORBIDDEN)

            with pytest.raises(exceptions.TransportError) as excinfo:
                credentials.sign_bytes(b"foo")
>           assert excinfo.match("{'error': {'code': 403, 'message': 'unauthorized'}")
E           AssertionError: Pattern "{'error': {'code': 403, 'message': 'unauthorized'}" not found in "Error calling sign_bytes: {'error': {'message': 'unauthorized', 'code': 403}}"

The order seems to change sometimes - I think loading the JSON into a dict would make the comparision stable.

I updated the test to just match 'code': 403 instead of the whole "{'error': {'code': 403, 'message': 'unauthorized'}") string so I don't need to do the JSON convertion.

I also noticed that python nox cover session always includes the google-auth bundled in /google-cloud-sdk/lib/third_party/ so I also updated the coveragerc to ignore that as well.